Preparation and characterization of novel environmentally sustainable mortars based on magnesium potassium phosphate cement for additive manufacturing

The "Digital Transition" of the building sector and in particular the concrete 3D printing is profoundly changing building technologies and construction processes. However, the materials engineering is still a challenge for the research of even more effective and performing 3D printable concrete. In this context, we analysed magnesium potassium phosphate cement (MKPC) performance as an innovative cementitious material in terms of sustainability and possibility of its use in extrusion-based 3D concrete printing (3DPC). Starting from common formulations present in literature, we discussed the relationship between water to binder ratio and workability in two different quantities of retarders. Some mix compositions were also prepared by replacing sand with rubber aggregates or glass aggregates with the aim of creating lightweight aggregate-based mortars. In addition, the fly ash (FA), a widely material used (but that will not be available in the next few years), was replaced with silica fume (SF). We found that two formulations (samples 2 and 7) show rheological requirements and compressive strengths at 90 min of respectively about 2 MPa and 3 MPa, which are deemed to be suitable for 3D printing processes. Moreover, in sample 7, the use of the expanded recycled glass as aggregate opens new possibilities for reducing the carbon footprint of the process.